<h2>DESCRIPTION</h2>

<i>r.sim.sediment</i> is a landscape scale, simulation 
model of soil erosion, sediment transport and deposition caused by flowing 
water designed for spatially variable terrain, soil, cover and  
rainfall excess conditions. The soil erosion model is based on the theory
used in the USDA WEPP hillslope erosion model, but it has been generalized
to 2D flow. The solution is based on the concept of duality between fields and 
particles and the underlying equations are solved by Green's 
function Monte  Carlo method, to provide robustness necessary for 
spatially variable conditions and high resolutions (Mitas and Mitasova 
1998).  Key inputs of the model include the following raster maps:
 elevation (<i>elevation</i> [m]), flow gradient given by the first-order partial 
derivatives of elevation field (<i> dx</i> and <i>dy</i>), 
overland flow water depth (<i>water_depth</i> [m]), detachment capacity coefficient 
(<i>detachment_coeff</i> [s/m]), transport capacity coefficient (<i>transport_coeff</i> [s]), 
critical shear stress (<i>shear_stress</i> [Pa]) 
and surface  roughness coefficient called Manning's n (<i>man</i> raster map). 
Partial derivatives can be computed by <a href="v.surf.rst.html">v.surf.rst</a>
or <a href="r.slope.aspect.html">r.slope.aspect</a>
module. The data are automatically converted from feet to metric
system using database/projection information, so the elevation always should be in meters. 
The water depth file can be computed using <a href="r.sim.water.html">r.sim.water</a>
module. Other parameters must be determined using field measurements or
reference literature (see suggested values in Notes and References). <br>

<p>
Output includes transport capacity raster map <i>transport_capacity</i>  in [kg/ms],
transport capacity limited erosion/deposition raster map
<i>tlimit_erosion_deposition</i> [kg/m<sup>2</sup>s]i that are output almost immediately and
can be viewed while the simulation continues. Sediment flow rate raster map 
<i>sediment_flux</i> [kg/ms], and net erosion/deposition raster map [kg/m<sup>2</sup>s]
can take longer time depending on time step and simulation time. 
Simulation time is controlled by <i>niterations</i> [minutes] parameter. 
<!-- Output files can be saved during simulation using <i>outiter</i> parameter
defining simulation time step for writing output files. This option requires
time series flag <i>-t</i>. Files are saved with suffix   containing
iteration number (e.g. name.500, name.1000, etc.) representing time in seconds.
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If the resulting erosion/deposition map is noisy, higher number of walkers,
given by <i>nwalkers</i> should be used. 
<br>

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<h2>NOTES</h2>
TODO: provide a table of suggested parameters for bare soil, grass, forest, pavement
wetland or pond, provide links to movies that explain the impact of the  parameters
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<h2>SEE ALSO</h2>

<a href="v.surf.rst.html">v.surf.rst</a>,
<a href="r.slope.aspect.html">r.slope.aspect</a>,
<a href="r.sim.water.html">r.sim.water</a>
                                                          
<h2>AUTHORS</h2>

Helena Mitasova, Lubos Mitas<br>
North Carolina State University<br>
<a href="mailto:hmitaso@unity.ncsu.edu">hmitaso@unity.ncsu.edu</a><br>
<br>
Jaroslav Hofierka<br>
GeoModel, s.r.o. Bratislava, Slovakia<br><address>
<a href="mailto:hofi@geomodel.sk">
hofierka@geomodel.sk</a>
</address>
<br>
Chris Thaxton<br>
North Carolina State University<br>
csthaxto@unity.ncsu.edu<br>
<address><a href="mailto:csthaxto@unity.ncsu.edu">
csthaxto@unity.ncsu.edu</a></address>

<h2>REFERENCES</h2>

<p>
<a href="http://www4.ncsu.edu/~hmitaso/gmslab/papers/II.6.8_Mitasova_044.pdf">
Mitasova, H., Thaxton, C., Hofierka, J., McLaughlin, R., Moore, A., Mitas L., 2004,</a>
Path sampling method for modeling overland water flow, sediment transport
and short term terrain evolution in Open Source GIS.
In: C.T. Miller, M.W. Farthing, V.G. Gray, G.F. Pinder eds.,
Proceedings of the XVth International Conference on Computational Methods in Water
Resources (CMWR XV), June 13-17 2004, Chapel Hill, NC, USA, Elsevier, pp. 1479-1490.
<p>
<a href="http://www4.ncsu.edu/~hmitaso/gmslab/gisc00/duality.html">
Mitasova H, Mitas, L., 2000, Modeling spatial processes in multiscale framework: 
exploring duality between particles and fields, </a>
plenary talk at GIScience2000 conference, Savannah, GA.
<p>
Mitas, L., and Mitasova, H., 1998, Distributed soil erosion simulation
for effective erosion prevention. Water Resources Research, 34(3), 505-516.
<p>
<a href="http://www4.ncsu.edu/~hmitaso/gmslab/papers/LLEmiterev1.pdf">
Mitasova, H., Mitas, L., 2001, Multiscale soil erosion simulations for land use management, </a>
In: Landscape erosion and landscape evolution modeling, Harmon R. and Doe W. eds.,
Kluwer Academic/Plenum Publishers, pp. 321-347.
<p>
<a href="http://www.grassbook.org">
Neteler, M. and Mitasova, H., 2008, Open Source GIS: A GRASS GIS Approach. Third Edition.</a>
The International Series in Engineering and Computer Science: Volume 773. Springer New York Inc, p. 406.
<p>
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